Abstract
SummaryA dynamic chamber method was developed to measure fluxes of N2O from soils with greater accuracy than previously possible, through the use of a quantum cascade laser (QCL). The dynamic method was compared with the conventional static chamber method, where samples are analysed subsequently on a gas chromatograph. Results suggest that the dynamic method is capable of measuring soil N2O fluxes with an uncertainty of typically less than 1–2 µg N2O‐N m−2 hour−1 (0.24–0.48 g N2O‐N ha−1 day−1), much less than the conventional static chamber method, because of the greater precision and temporal resolution of the QCL. The continuous record of N2O and CO2 concentration at 1 Hz during chamber closure provides an insight into the effects that enclosure time and the use of different regression methods may introduce when employed with static chamber systems similar in design. Results suggest that long enclosure times can contribute significantly to uncertainty in chamber flux measurements. Non‐linear models are less influenced by effects of long enclosure time, but even these do not always adequately describe the observed concentrations when enclosure time exceeds 10 minutes, especially with large fluxes.
Highlights
Nitrous oxide (N 2 O) is a potent greenhouse gas (GHG) and the single largest contributor to global stratospheric ozone depletion (Ravishankara et al, 2009)
Gas samples are extracted from a chamber sealed on the soil surface during a 30–60 minute incubation period, and later analysed using a gas chromatograph (GC) instrument
In this paper we describe the system design, the analysis of the high-resolution data obtained, and comparison with conventional static chamber measurements
Summary
Nitrous oxide (N 2 O) is a potent greenhouse gas (GHG) and the single largest contributor to global stratospheric ozone depletion (Ravishankara et al, 2009). Global N 2 O fluxes have large uncertainties associated with them (55–75 %) (IPCC, 2007) because of the large temporal and spatial variability of N 2 O fluxes, and the uncertainty inherent in the methodology predominantly used to measure them (Folorunso & Rolston, 1985; Velthof et al, 1996). Almost all measurements use the closed, non-steady-state (or ‘static’) chamber method (Hutchinson & Mosier, 1981), because of its simplicity and small cost In this method, gas samples are extracted from a chamber sealed on the soil surface during a 30–60 minute incubation period, and later analysed using a gas chromatograph (GC) instrument. Because of the constraints imposed by the logistics of extracting samples and subsequent laboratory analysis, the sample size is typically limited to
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